Stepping motor

ABSTRACT

The present invention is a stepping motor used as a driving source for stepping movement of autmatic-machine members. Diodes are connected to the terminal side of a DC power source in a forward direction to prevent accumulated magnetic energy from returning to the power source. A high-voltage large current due to reduction of magnetic energy rushes into an exciting coil to be excited, the magnetic energy of the exciting coil quickly decreases, and a high-speed stepping operation is exeuted. Moreover, the digital signal of each address in a ROM corresponding to the number of steps is read, the read digital signal is converted into an analog signal, acceleration is executed by the frequency of the stepping electric signal corresponding to the frequency proportional to the analog signal for the shortest time without outstepping, and deceleration is executed for the shortest time by reading the ROM backward when the number of steps is halved. 
     Therefore, the numerical control of load movement can be executed for a shortest time without outstepping.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stepping motor used as a drivingsource for stepping movement of automatic-machine members.

2. Description of the Related Art

Though a stepping motor using a magnet rotor is already known in theart, it has disadvantages of small output torque and stepping speed.

When increasing the output torque, the stepping speed decreases. Toperform the specified operation stepping at a high speed withoutoutstepping, the prior art slowly increases the frequency of thestepping electric signal and slowly decreases it to step. However, theprior art has many problems including that the electric circuit iscomplicated and expensive and it is difficult to obtain a satisfactoryperformance.

For one stepping operation, one exciting coil is turned off, theaccumulated magnetic energy is discharged, and magnetic energy isaccumulated when the next exciting coil is turned on. Discharge andaccumulation of the magnetic energy requires time. For a large outputtorque, the stepping time increases and high-speed stepping isimpossible because large magnetic energy is accumulated.

To avoid the above-mentioned disadvantage, means is provided to executehigh-speed stepping by raising the applied voltage to quickly accumulatemagnetic energy and returning the accumulated magnetic energy to thepower source to quickly decrease it. However, the means has thefollowing two disadvantages. First, the means cannot be used under a lowvoltage because the applied voltage is too high.

Secondly, because the means is limited to high-speed stepping, it isimpossible to achieve a higher-speed stepping operation.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a stepping motor havinga large output torque and having a simplified circuit configurationcapable of performing the specified stepping operation at a high speedwithout outstepping.

The present invention is a reluctance-type motor comprising an n-phase(n=2, 3, 4, . . . ) full-wave rotor having salient poles, n-phaseexciting coils installed on n-phase magnetic poles, semiconductorswitching devices connected to both sides of the first, second, third, .. . , and n-th phase exciting coils configured into the first andfirst-bar exciting coils, the second and second-bar exciting coils, thethird and third-bar exciting coils, . . . , and n-th bar exciting coils,respectively, diodes inversely connected to a serially-connected body ofthe exciting coils corresponding to the semiconductor switching devices,a DC power source for apply voltage to the exciting coils through thesemiconductor switching devices, the first and first-bar exciting coilsexcited by the first backflow-preventive diode connected to the positivepole of the DC power source in the forward direction, an excitationcontrol circuit consisting of the second and second-bar exciting coils,the third and third-bar exciting coils, . . . , and n-th and n-th-barexciting coils respectively excited by the similarly-connected second,third, . . . , and n-th backflow-preventive diodes, aspecified-frequency n-phase full-wave stepping electric-signalgenerator, and an electric circuit to generate stepping torque byelectrifying the semiconductor switching devices respectively connectedto the first, second, third, . . . , and n-th phase exciting coils bythe stepping electric signal. Furthermore, the present invention is areluctance-type stepping motor.

The reluctance-type stepping motor of the present invention comprises ann-phase (n=3, 4, 5, . . . ) half-wave rotor having salient poles,n-phase exciting coils installed on n-phase magnetic poles,semiconductor switching devices connected to both sides of the first,second, third, . . . , and n-th phase exciting coils respectivelyconfigured into the first, second, third, . . . , and n-th excitingcoils, diodes inversely connected to a serially-connected body of theexciting coils corresponding to the semiconductor switching devices, aDC power source apply voltage to the exciting coils through thesemiconductor switching devices, the first exciting coil excited by thefirst backflow-preventive diode connected to the positive pole of the DCpower source in the forward direction; an excitation control circuitincluding the second, third, . . . , and n-th exciting coilsrespectively excited by the similarly-connected second, third, . . . ,and n-th backflow-preventive diodes, and first, second, third, . . . ,and n-th small-capacity condensers connected between the outpot side ofthe backflow preventive diodes and the negative side of the DC powersource, a specified-frequency n-phase half-wave stepping electric-signalgenerator, and an electric circuit to generate stepping torque byelectrifying the semiconductor switching devices connected torespectively-corresponding first, second, third, . . . , and n-th phaseexciting coils by the stepping electric signal. Furthermore, the presentinvention comprises, in the first or second means, a steppingelectric-signal generator consisting of a memory circuit to memorize thespecified number of steps, an electric circuit to input the number ofsteps to the first counting circuit and half the number of steps to thesecond counting circuit, an electric circuit to start subtraction of thefirst and second counting circuits according to the the number of steps,read the digital memory stored in a ROM, and inversely read the digitalmemory of the ROM by the zero-count output signal of the second countingcircuit when the stepping motor starts, an oscillation circuit toconvert the read signal of the ROM into an analog signal to obtain thefrequency of the oscillation pulse proportional to the analog signal, apulse distributor to output an n-phase full- or half-wave steppingelectric signal by inputting the frequency of the output oscillationpulse of the oscillation circuit, and an electric circuit to startinputting the output stepping electric signal of the pulse distributorto the excitation control circuit of the motor by the driving startcommand electric signal of the reluctance-type stepping motor and tostop inputting the oscillation-circuit pulse to the pulse distributorwhen the first counting circuit counts zero.

Furthermore, the present invention includes a stepping motor comprisingan n-phase (n=2, 3, 4, . . . ) full-wave magnet rotor, n-phase excitingcoils installed on n-phase magnetic poles of a fixed armature, anexcitation control circuit including several sets of transistorsincluding exciting coils of various phases, diodes inversely connectedto each transistor of the circuit in parallel to return magnetic energyto the power supply side when exciting coils are turned off, a DC powersource to apply voltage to the excitation control circuit, an electriccircuit to supply power to the excitation control circuit includingseveral sets of transistors through "n" backflow-preventive diodesconnected to the DC power source in the forward direction, aspecified-frequency n-phase full-wave stepping electric-signalgenerator, and an apparatus to generate stepping torque by electrifyingthe excitation control circuit including several sets of transistorshaving corresponding first, second, third, . . . , and n-th excitingcoils by said stepping electric signal.

Furthermore, the present invention is a stepping motor comprising

an n-phase (n=3, 4, 5, . . . ) half-wave magnet rotor, n-phase excitingcoils installed on n-phase magnetic poles of a fixed armature,transistors connected to both sides of the exciting coils, diodesconnected to a serially-connected body of said exciting coilscorresponding to said transistors, a DC power source to apply voltage toexciting coils through the transistors, an excitation control circuit torespectively electrify n-phase exciting coils through "n"backflow-preventive diodes connected to the DC power source in theforward direction, "n" condensers with the specified capacity connectedbetween the output sides of the backflow-preventive diodes and thenegative pole of the DC power source, a specified-frequency steppingelectric-signal generator, and an electric circuit to generate steppingtorque by electrifying the transistors connected to the both sides ofrespectively-corresponding n-phase exciting coils by said steppingelectric signal.

Furthermore, the present invention comprises, in the fourth or fifthmeans, a stepping electric-signal generator including a memory circuitto memorize the specified number of steps, an electric circuit to inputthe number of steps to the first counting circuit and half the number ofsteps to the second counting circuit; electric means to startsubtraction of the first and second counting circuits according to thenumber of steps, read the digital memory stored in a ROM, and executebackward reading the digital memory of the ROM by the zero-count outputsignal of the second counting circuit when the stepping motor starts, anoscillation circuit to convert the read signal of the ROM into an analogsignal to obtain the frequency of the oscillation pulse proportional tothe analog signal, a pulse distributor to output n-phase full- orhalf-wave stepping electric signals by inputting the frequency of theoutput oscillation pulse of the oscillation circuit and an electriccircuit to start inputting the output stepping electric signal of thepulse distributor to the excitation control circuit of the motor by thedriving start command electric signal of the stepping motor and to stopinputting the oscillation-circuit pulse to the pulse distributor whenthe first counting circuit counts zero.

According to the present invention, when a diode is connected to apositive or negative terminal of an applied DC power in the forwarddirection and the accumulated magnetic energy is prevented fromreturning to the power source, a large high-voltage current due to adecrease of magnetic energy rushes into the exciting coil to be nextexcited, rapid accumulation of magnetic energy is completed, and themagnetic energy of the preceding exciting coil quickly decreases.Therefore, a high-speed stepping operation is realized.

If a time lag is present between the end of excitation of the precedentexciting coil and start of excitation of the next exciting coil, thesame purpose can be realized by temporarily charging magnetic energy ina condenser with a small capacity (0.1 to 0.3 uF).

As the result of measurement, magnetic energy can be moved at the outputof at approx. 300 W for approx. 20 microseconds. Therefore, a steppingmotor with a large output torque and rotational speed can be obtained.

As mentioned later about FIG. 4, with respect to FIG. 4 the digitalsignal quantity in each address of the ROM corresponding to the numberof steps is read, the digital signal is converted into an analog signal,acceleration is executed for the shortest time by the stepping electricsignal corresponding to the frequency proportional to the analog signalwithout outstepping, and deceleration is executed for the shortest timeby inversely reading the ROM when the number of steps is halved.

Therefore, load movement can be numerically controlled for the shortesttime without outstepping.

Thus, the control circuit can be simplified because the first effect isobtained only by adding a diode and small-capacity condenser to thepower source side. Also, the applied DC voltage can be decreased.

Moreover, the load can be numerically controlled at the maximum speedwithout outstepping.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a), 1(b), and 1(c) show are a schematic diagrams of the magneticrotor, the magnetic pole and exciting coil according to the presentinvention:

FIGS. 2(a) through 2(d) are the excitation control circuits accrding tothe present invention;

FIG. 3 is a block circuit diagram of the stepping electric-signalgenerator;

FIG. 4 is a stepping electric-signal generator circuit diagram tonumerically control the load for the shortest time;

FIG. 5 is graph of the number of pulses and pulse oscillation frequencyof the circuit shown in FIG. 4; and

FIGS. 6(a) and 6(b) are time charts showing the curves of the steppingelectric signal, output torque, and exciting current.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A following is the description of embodiments of the present inventionaccording to FIGS. 1(a), 1(b), and 1(c).

FIG. 1(a) is a sectional view showing the configurations of the salientpoles of the rotor and of magnetic poles and exciting coils of the fixedarmature of a 2-phase reluctance-type stepping motor to which thepresent invention is applied.

All subsequent angles are shown in electrical angles.

The salient poles 1a, 1b, etc. of the rotor 1 have a width of 180°respectively and are arranged at equal pitch with a phase difference of360°.

The rotor 1 is a known means in which silicon steel plates are laminatedand include the rotary shaft 5.

The balls of the ball bearing 4 are not illustrated.

The magnetic poles 16a, 16b, etc. are made by the same means as that ofthe rotor 1 together with the fixed-armature magnetic core 16 to serveas a magnetic path.

The protruded teeth 16a-1, 16a-2, are installed on the ends of themagnetic poles 16a, 16b, etc. respectively. The teeth have a width of180° and are separated by equal angles.

The exciting coils 17a, 17b, etc. are set to the magnetic poles 16a,16b, etc. which are arranged on the peripheral surface at an equal pitchas shown in FIG. 1(a).

FIG. 1(b) is development of the magnetic pole and salient pole.

The cooling fins 6a, 6b, etc. in FIG. 1(a) are used for radiating heat.A base 6 is fitted to the outside of the fixed armature 16.

The outer cylinder 21 serves as a cover of the cooling fins 6a, 6b, etc.

The round holes 21a, 21b, etc. are tapped holes for fastening withmachine screws.

The following is a detailed description of the sectional view of FIG.1(a) and the development in FIG. 1(b).

The annular ring 1l and magnetic poles 16a, 16b, etc., are known in theart and in which silicon steel plates are laminated and secured,configuring a fixed armature. The magnetic core 16 serves as a magneticpath.

The exciting coils 17a, 17b, etc. are set to the magnetic poles 16a,16b, etc. The salient poles 1a, 1b, etc. are installed on the peripheryof the rotor 1, which face the teeth 16a-1, 16a-2, etc. of the magneticpoles 16a, 16b, etc. with a gap of 0.1 to a 0.2 mm. The tooth width isequal to salient-pole width. The separation angle between teeth is 180°.

For the teeth 16a-1, 16a-2, 16a-3, etc. in FIG. 1(b), three teeth areused for one magnetic pole. However, two or more than three teeth can beused for one magnetic pole.

The output torque increases, the stepping angle decreases, and theresolution is improved proportionally to the number of teeth permagnetic pole.

When the exciting coils 17a and 17e (a serially- or parallely-connectedbody of both coils is called the exciting coil K) are excited, the teethand salient poles are attracted to each other. At the same time,exciting coils 17b and 17f (a serially- or parallely-connected body ofboth coils is called the exciting coil M) are excited.

Therefore, the exciting coils are driven by a specified angle from theposition shown in FIG. 1(b) in the direction of the arrow and stop.

The stop point is the point where the reverse torque due to the magneticpoles 16a and 16e is balanced with the normal torque due to the magneticpoles 16b and 16f.

In the time chart of FIG. 6, the former torque curve is shown as thecurve 39a and the latter torque curve is shown as the curve 39b.

The broken line represents the reverse torque and the above-mentionedbalance point is the point on the straight line 40. Though the point onthe straight line 40 depends on the shape of the torque curve, a torquecurve shape is preferable in which the return torque increases when therotor 1 is horizontally deviated.

Therefore, the above-mentioned object is achieved by changing the shapeof the facing plane between a salient pole and a tooth. When theexciting coils 17a and 17e are turned off, the exciting coils 17c and17g (a connected body including both coils is called the exciting coilL) are excited and the rotor 1 rotates by 90° and stops.

When the exciting coils 17b and 17f are turned off, the exciting coils17d and 17h (a connected body including both coils is called theexciting coil N) are excited.

As mentioned above, a 2 phase full-wave stepping motor with one step of90° is obtained.

FIG. 1 (c) is a development of the 2-phase full-wave stepping motor towhich the present invention is applied, showing the configurations ofthe N and S magnetic poles of the rotor, the magnetic pole of the fixedarmature, and the exciting coil.

All subsequent angles are shown in electrical angles.

The N and S magnetic poles 1a, 1b, etc. having a width of 180° arealternately arranged on the magnet rotor 1.

The same-phase magnetic poles 3a and 3b are separated from each other by180° in mechanical angle and the same-phase magnetic poles 4a and 4bseparate from each other by 90° in phase and are installed on the fixedarmature 4.

Three teeth (salient poles) separated from one another by the samedistance are protrusively installed on the magnetic poles 3a and 4arespectively as shown in the FIG. 1 (c) which have the same width as themagnetic poles 1a, 1b, etc. and are separated from each other by thesame distance.

The magnet rotor 1 is an introversion type and rotatably supported by arotary shaft (not illustrated).

The fixed armature 4 is configured by a known means in which siliconsteel plates are laminated and fixed.

The exciting coils 16a, and 16b, are set to magnetic poles 3a and 3b,and the exciting coils 17a and 17b are set to the magnetic poles 4a and4b.

The embodiment in FIG. 1 (c) uses the teeth 5a, 5b, and 5c, and theteeth 6a, 6b, and 6c for one magnetic pole respectively. However, twoteeth or more than three teeth can be used for each magnetic pole.

The output torque increases, the stepping angles decrease, and theresolution is improved proportionally to the number of teeth permagnetic pole.

When the exciting coils 16a, and 16b, in FIG. 1 (a serially-orparallely-connected body of both coils is called the exciting coil K)are excited, and teeth and magnetic poles are attracted or repelled.

At the same time, the exciting coils 17a and 17b (a connected body ofboth coils is called the exciting coil L) are excited. Therefore, theyare driven by the specified angle from the position shown in FIG. 1 inthe direction of the arrow and stop.

The stop point is the point where the reverse torque due to the magneticpoles 4a and 4b is balanced with the normal torque due to the magneticpoles 3a and 3b.

In the time chart of FIG. 6 (a) or 6 (b), the former torque curve isshown as the curve 39a and the latter torque curve is shown as the curve39b.

The broken line represents the reverse torque and the above-mentionedbalance point is the point on the straight line 40. Though the point onthe straight line 40 depends on the shape of the torque curve, a torquecurve shape is preferable in which the return torque increases when therotor 1 is horizontally deviated.

Then, because the exciting direction of the exciting coils 17a and 17bis reversed, normal torque is generated, the magnet rotor rotates by 90°and stops when the normal torque is balanced with the reverse torque dueto the magnetic poles 3a and 3b.

As mentioned above, a 2-phase full-wave stepping motor to performstepping every 90° is obtained by repeatedly exciting the exciting coils16a and 16b and the exciting coils 17a and 17b.

The following is a detailed description of excitation control of theexciting coils K, L, M, and N according to FIG. 2(a).

In FIG. 2(a), the inputs of the terminals 3a, 3b, and 3c receive thestepping electric signal which can be obtained from the known circuitshown in FIG. 3.

In FIG. 3, the block circuit 13 is an oscillator which outputs electricpulses with the specified frequency. The output electric pulse is inputto the pulse distributor 14 and then output as a 2-phase full-wavestepping electric signal from the terminals 15a, 15b, 15c, and 15d.

The outputs of the terminals 15a, 15b, etc. are input to the terminals3a, 3b, etc. in FIG. 2(a) respectively.

The inputs of the terminals 3a (exciting coil K) and 3b (exciting coilL) are shown as the curves 35a, and 35b, and the curves 36a and 36b inthe time chart of FIG. 6(a).

The inputs of the terminals 3c (exciting coil M) and 3d (exciting coilN) are shown as the curves 37a and 37b and the curves 38a and 38b inFIG. 6(a) whose phase is delayed by 90°.

Because the transistors 7a and 7b are turned on by the electric signalof the curve 35a input to the terminal 3a, the exciting coil K excited.After a certain time elapses, because the electric signal of the curve37a is input from the terminal 3c, the transistors 8a and 8b are turnedon and the exciting coil M is excited.

Therefore, as previously mentioned about the torque curves 39a and 39b,the coil stops at a point on the straight line 40. Then, because theelectric signal of the curve 36a is input from the terminal 3b, thetransistors 7c and 7b are turned on and the exciting coil L is excited.

In this case, because the input of the terminal 3a is simultaneouslydisconnected, the transistors 7a and 7b are turned off.

According to a known means, the magnetic energy accumulated in theexciting coil K is returned to the power source through the diodes 11cand 11b. Therefore, it is impossible to decrease the reduction time ofthe magnetic energy unless the applied voltage is raised.

If the source voltage is raised, the exciting coil current excessivelyincreases and burning occurs.

If a rapid stepping operation is executed, reverse torque is generateddue to the discharge current of magnetic energy and the output torque isdecreased.

Moreover, because start of excitation of the exciting coil L to be nextexcited is delayed, torque is decreased.

The apparatus of the present invention has the effect to eliminate theabove problems by adding the diode 9a shown in FIG. 2(a).

That is, because the power of the exciting coil K is disconnected,discharge of the accumulated magnetic energy is interrupted by the diode9a, a high voltage is applied to the exciting coil L through thetransistors 7c and 7d which are simultaneously turned on and magneticenergy is quickly accumulated.

The curves 41a, 41b, 41c, and 41d in FIG. 6(a) show the excitationcurves of the exciting coils K and L.

The width between the trailing edge of the curve 41a (current of theexciting coil K) and the leading edge of the curve 41b (current of theexciting coil L) becomes equal to the width between the broken lines 42aand 42b and the curves become very steep.

It takes 30 microseconds for a motor with an output of 300 W. Therefore,even if the stepping frequency is increased, no reverse or decreasetorque mentioned above is generated. Thus, high-speed stepping isrealized without problems.

Moreover, a low voltage can be used for the voltage between thepower-source terminals 2a and 2b because only the specified excitingcurrent may be supplied exceeding the counter electromotive force.

Also for excitation of the exciting coils M and N according to thecurves 37a and 37b and the curves 38a and 38b in FIG. 6, theabove-mentioned effect is the same. The diode 9b also has the sameeffect as the diode 9a.

Though the condensers 10a and 10b are not always necessary, they protecttransistors if there is any difference between the turning-on/offtimings.

Though this embodiment describes a 2-phase full-wave stepping motor, itcan also be applied to 3-phase, 4-phase, . . . , and n-phase full-wavestepping motors.

In this specification, the first-phase exciting coils K and L areconsidered as the first and first-bar exciting coils and thesecond-phase exciting coils M and N are considered as the second andsecond-bar exciting coils. The same is true for a case in which thenumber of phases increases.

The following is a description of an excitation control circuit of a3-phase half-wave reluctance-type stepping motor according to FIG. 2(b).

Input signals of the stepping motor input from the terminals 3a, 3b, and3c are obtained from a known oscillator and pulse distributor. Inputsignals of the terminals 3a, 3b, and 3c are shown as the electric signalcurves 43a and 43b, the curves 44a and 44b, and the curves 45a and 45brespectively.

The curves 43a, 44a, and 45a have a phase delay of 120° respectively.

The exciting coils P, Q, and R are installed on six magnetic polesrespectively and every two poles are symmetrically arranged. Therefore,six combinations of the magnetic poles and an exciting coil are made andthe exciting coils are arranged at the periphery with a separation of60° in mechanical angle.

When the stepping electric signal is input from the terminals 3a and 3b,the transistors 7a, 7b, 7c, and 7d are turned on and the exciting coilsP and Q are excited. The rotor is driven and stops at the specifiedposition.

Then, when the input signal to the terminal 3a disappears, the rotorrotates by the specified angle and stops because the signal is input tothe terminal 3c. The stepping angle becomes 120°.

Exciting coils are excited in order of P, Q→Q, R→R, P→P, Q→.

When the electric signal of the curve 43a disappears which is the inputsignal to the terminal 3a, the magnetic energy is not returned to thepower source but it is accumulated in the condenser 10a because thediode 9a is connected. By decreasing the capacity of the condenser to avalue corresponding to the inductance of the exciting coil P, it ischarged at a high voltage.

Therefore, the magnetism of the exciting coil P quickly decreases. Aftera certain time elapses, the exciting coil P is excited again by theelectric signal of the curve 43b. In this case, the exciting currentquickly rises due to the high voltage of the condenser 10a.

The exciting coils Q and R, the diodes 9b and the 9c, and condensers 10band 10c have the same effect.

Thus, high-speed stepping is realized at a low source voltage. Thisembodiment describes a 3-phase half-wave stepping motor. However, it canalso be applied to 4-, 5-, . . . , and n-phase stepping motors,realizing the same effect.

The exciting coil of the first phase is called the first exciting coil,and the exciting coils of the second and third phases are called thesecond and third exciting coils, respectively.

As mentioned above, according to the apparatus of the present invention,the reluctance-type stepping motor having a large output torquecorresponding to a high stepping frequency can be obtained. Therefore,an effective technical means can be obtained because a low sourcevoltage can be used.

The following is a description of an embodiment of a 5-phase half-wavestepping motor of the present invention according to FIG. 2(c).

The exciting coils P, Q, R, S, and T installed on a 5-phase magneticpole function as the first-, second-, . . . , and fifth-phase excitingcoils respectively.

The stepping electric signals are output from the terminals 12a, 12b,etc. in FIG. 6(a) when the transistors 7a and 7b are turned on and theexciting coil P is excited.

Electric pulses with the specified frequency are input to the pulsedistributor 14 from the oscillator 13 and the stepping electric signalsfrom the output terminals 12a, 12b, . . . , and 12e are shown as thecurves 46a and 46b, the curves 47a and 47b, the curves 48a and 48b, thecurves 49a and 49b, and the curves 50a and 50b, respectively in FIG.6(a).

The phases of the curves 46a, 47a, 48a, 49a, and 50a are sequentiallydelayed by 72°. The curves have a width of 180° respectively and areseparated by the same angle from one another.

The transistors 7c, 7e, and 7f are turned on by the stepping electricsignals from the terminals 12b and 12c and the exciting coils Q and Rare excited.

The block circuits S-1 and T-1 control the exciting coils S and T, whichhave same configuration as that of the excitation control circuit forthe exciting coil P.

Therefore, the exciting coils S and T are excited by the steppingelectric signals from the terminals 12a and 12e.

When the exciting coils P, Q, and R are excited, the rotor stops at thepoint past the right end of the curve 46a. When the exciting coils Q, R,and S are excited, the rotor stops at the point past the right end ofthe curve 47a.

The rotor 1 is driven by the fact that excitation is repeated in orderof the exciting coils P, Q, and R, exciting coils Q, R, and S, excitingcoils R, S, and T, exciting coils S, T, and P, exciting coils T, P, andQ, and exciting coils P, Q, and R.

The exciting coils excited when the output electric pulse of theoscillator in FIG. 6(a) is stopped are shown below only by theirsymbols, (P, Q), (P, Q, R), (Q, R), (Q, R, S), (R, S), (R, S, T), (S,T), (S, T, P), (T, P), (T, P, Q).

Therefore, one cycle is completed in 10 steps with a stepping angle of36°.

The exciting coils P, Q, R, S, and T are installed on 10 magnetic polesrespectively. Every two poles are symmetrically arranged andsimultaneously excited.

Therefore, ten combinations of the magnetic poles and an exciting coilare made and the exciting coils are arranged at periphery with a theseparation angle (mechanical angle) of 36°.

When the electric signal of the curve 46a disappears which is the outputsignal of the terminal 12a, the magnetic energy is not returned to thepower source but is accumulated in the condenser 10a because the diode10a is connected. By decreasing the capacity of the condenser to a valuecorresponding to the inductance of the exciting coil P, it is charged ata high voltage.

Therefore, the magnetism of the exciting coil P quickly decreases. Aftera certain time elapses, the exciting coil P is excited again by theelectric signal of the curve 46b. In this case, the exciting currentquickly rises due to the high voltage of the condenser 10a. Thus, ahigh-speed stepping motor with a large output torque is realized.

The diodes, 9b, 9c, 9d, and 9e and the condensers 10b, 10c, 10d, and 10efor excitation control of the exciting coils Q, R, S, and T have thesame effect.

It is the same as the embodiment in FIG. 2(b) that the condensers 10a,10b, . . . , and 10e serve as necessary parts.

Other effects are the same as those of the embodiment in FIG. 2(b).

In FIGS. 2(a), 2(b), and 2(c), the diodes 9a, 9b, 9c, etc. are installedat the positive pole 2a side of the power source.

However, the same effect is also obtained by removing these diodes,applying voltage to each exciting coil from the positive pole 2a side ofthe power source, and independently applying the exciting current ofeach exciting coil to the negative pole 2b of the power source through adiode.

The following is a description of a numerical control driving means fora higher-speed load shown in FIG. 4.

The computer 18 stores the necessary number of types of numerical valuesfor numerical control of a load.

When the electric signal to command the number of pulses for loadcontrol of N pulses is input from the terminal 18a, N pulses are outputfrom the terminal 19a and counted by the counting circuit 22a. At thesame time, 1/2 N pulses are output from the terminal 19b and counted bythe counting circuit 22b.

A set signal is input from the terminal 22 and each counting circuit isreset to 0 before the above counting operation starts.

The voltage of the terminal 23 is divided by the resistances 30a and 30band the divided voltage is used as the base voltage of the transistor29b.

Therefore, the base current set to the transistor 29a flows and thecondenser 28 is charged by a current proportional to the base current.

The transistors 29a and 29b are operated in the active region.

When the charged voltage reaches the specified value, the trigger diode31 is turned on to start discharge.

Therefore, a pulse oscillating circuit is made and its oscillationfrequency increases proportionally to the base current of the transistor29b.

The output of the pulse oscillating circuit is input to the pulsedistributor 14 through the AND circuit 14a and the output of thedistributor is output from the terminals 15a, 15b, etc.

The output of the terminal 15a, 15b, etc. is the same as that of theterminals with the same symbol previously mentioned in FIG. 3, whichserves as a 2-phase full-wave stepping electric signal.

Therefore, by using the output for the input of the terminals 3a, 3b,etc. of the armature-current control circuit in FIG. 2(a), one step isexecuted for each output pulse of the AND circuit 14a.

The pulse distributor generally uses a circuit containing three JK-typeflip-flop circuits.

To start driving the stepping motor, pulse electric signals are inputfrom the terminals 24c and 24d.

The pulse electric signal brings the outputs of the terminal Q of theflip-flop circuit 24a and the terminal Q-bar of the flip-flop circuit24b to a high level.

Because the upper-side input of the AND circuit 14a becomes high-level,the output of the pulse oscillating circuit is input to the pulsedistributor 14 to start the stepping motor. The resistances 30a and 30bare selected so that the oscillation pulse frequency in this case willbe the self-starting frequency. Also, because the lower-side input ofthe AND circuit 27a becomes high-level, the output (oscillation pulse)of the AND circuit 14a is input to the terminal "c" of the countingcircuit 22c (which is already reset to 0 by the input of the terminal R)and counted up.

The set digital values are previously memorized in each address of theROM 25.

Whenever data is counted up by the counting circuit 22c, the digitalmemory of the adress corresponding to each count is read and input tothe D-A converting circuit 26, and the analog signal corresponding tothe digital memory is output. This output slowly increases the voltagedrop of the resistance 30b.

Therefore, because the base current of the transistor 29acorrespondingly increases and the frequency of the pulse oscillatingcircuit also increases, the stepping motor is accelerated.

For acceleration, each constant of the electric circuit and digitalmemory of the ROM 25 are selected so that the motor speed will bemaximized within the range in which no outstepping occurs.

As previously mentioned, the stepping motor of the present invention hasa limit for the maximum speed.

When the oscillation frequency of the oscillation circuit approaches thelimit for the maximum speed, the digital memory of the ROM 25 and thepulse oscillation frequency of the oscillation circuit are kept at acertain value respectively.

Therefore, the speed of the stepping motor is correspondingly keptconstant. When the number of output pulses of the AND circuit decreasesto 1/2 N pulses, subtraction is executed by the input of the terminalc-bar of the counting circuit 22b.

Therefore, the counting circuit 22b is set to 0, the terminal R of theflip-flop circuit 24a is electrified and reversed, the high-level outputof the terminal Q-bar serves as the lower-side input of the AND circuit27b, the lower-side input becomes high-level, and the output pulse ofthe AND circuit 27 can be obtained. The output of the AND circuit 27a isdisconnected.

Therefore, because the counting circuit 22c is subtracted by the inputpulse from the terminal c-bar, addresses of the ROM 25 are readbackward, the output voltage of the D-A converting circuit 26 slowlydecreases, and the pulse frequency of the oscillation circuit alsoslowly decreases.

Therefore, the stepping motor is decelerated.

The above-mentioned acceleration and deceleration are symmetricallyexecuted. It is also necessary to prevent out-stepping for deceleration.

The output pulse of the AND circuit 14a is subtracted because it is alsoinput to the terminal c-bar of the counting circuit 22a.

When N steps of the stepping motor are completed, the counting circuit22a is reset to 0. The output is reversed because it is input to theterminal S of the flip-flop circuit 24b, the upper-side input of the ANDcircuit 14a is changed to a low level, and the change of the output ofthe pulse distributor 14 is stopped.

Therefore, the stepping motor stops, and the load, executed by N stepsis stopped and held by the locking torque.

The graph in FIG. 5 shows the relation between the number of oscillationpulses (abscissa) which is the output of the AND circuit 14a and thepulse oscillation frequency (ordinate).

The stepping motor starts at the self-starting frequency F (shown by thestraight line 34) and slowly increases the speed as shown by thestepping frequency curve 32. The motor is accelerated up to the maximumspeed free from outstepping. The curve 32 levels off at the limit speedand the speed is kept at the maximum speed.

After 1/2 N steps are executed, the motor speed reaches the point on thebroken line B and then decreases as shown by the curve 33c and the motorstops.

The broken line B is symmetric for the right and left (portion parallelto the curve 33c) of the curve 32.

If the number of steps N for numerical control is small, the motor isdecelerated and stops as shown by the curve 33a because 1/2 N steps arecompleted at the leading edge of the curve 32.

For larger number of steps, the motor is decelerated and stops as shownby the broken line 33b.

The stepping speed control according to the present invention ischaracterized by the fact that numerical control of the load is alwaysexecuted for the minimum time even if the number of steps is changed.

The following is a detailed description of excitation control of theexciting coils K and L according to FIG. 2(d).

The input of the terminals 12a, 12b, 12c, and 12d is the stepping signalwhich can obtained by the known circuit shown in FIG. 3.

In FIG. 3, the block circuit 13 is an oscillator which oscillateselectric pulses with the specified frequency. The output electric pulseis input to the pulse distributor 14 and a 2-phase full-wave steppingelectric signal is output from the terminals 15a, 15b, 15c, and 15d.

The outputs of the terminals 15a, 15b, etc. are input to the terminals12a, 12b, etc. in FIG. 2(b) respectively.

Inputs of the terminals 12a and 12b are shown as the curves 35a and 35band the curves 36a and 36b in the time chart of FIG. 6(b).

The inputs of the terminals 12c and 12d are shown as the curves 37a and37b and the curves 38a and 38b in FIG. 6(b) whose phase is delayed by90°.

Because the transistors 7a and 7b are turned on by the electric signalof the curve 35a input to the terminal 12a, the exciting coil K isexcited rightward. When the electric signal of the curve 37a is inputfrom the terminal 12c after a certain time elapses, the transistors 8aand 8b are turned on and the exciting coil L is excited.

Therefore, the coil stops at the point where normal torque is balancedwith reverse torque as previously mentioned about the torque curves 39aand 39b.

Then, because the electric signal of the curve 36a is input from theterminal 12b, the transistors 7c and 7d are turned on and the excitingcoil K is excited leftward.

At the same time, because the input of the terminal 12a is disconnected,the transistors 7a and 7b are turned off.

The magnetic energy accumulated in the exciting coil K is returned tothe power source from the terminals 2a and 2b through the diodes 11c and11d according to a known means.

Therefore, it is impossible to decrease the reduction time of themagnetic energy unless the applied voltage is raised.

If the source voltage is raised, the exciting coil current excessivelyincreases and burning occurs.

If a stepping operation is suddenly executed, reverse torque isgenerated by the discharge current of magnetic energy and the outputtorque is decreased.

Moreover, because start of excitation of the exciting coil L to be nextexcited is delayed, the torque is decreased.

The apparatus of the present invention has the effect to eliminate theabove problems by adding the diodes 9a and 9b shown in FIG. 2(b).

That is, when excitation of the exciting coil K is stopped by thetransistors 7a and 7b, discharge of accumulated magnetic energy isinterrupted by the diode 9a. Therefore, high voltage rushes into theexciting coil K through the transistors 7c and 7d which are also turnedon and magnetic energy is rapidly accumulated.

The curves 41a, 41b, 41c, and 41d in FIG. 6(b) show the curve forreciprocal excitation of the exciting coil K.

The width between the trailing edge of the curve 41a (rightward currentof the exciting coil K) and the leading edge of the curve 41b (leftwardcurrent of the exciting coil L) becomes equal to the width between thebroken lines 42a and 42b and the curves become very steep.

It takes 20 microseconds for a motor to output of 300 W. Therefore, evenif the stepping frequncy is increased, no reverse or decrease torquementioned above is generated. Thus, high-speed stepping is realizedwithout problems.

Moreover, a low voltage can be used for the voltage between thepower-source terminals 2a and 2b because only the specified excitingcurrent may be supplied exceeding the counter electromotive force.

Also for reciprocal excitation of the exciting coil L according to thecurves 37a and 37b and the curves 38a and 38b in FIG. 6(b), theabove-mentioned effect is the same. The diode 9b also has the sameeffect as the diode 9a.

The condensers 10a and 10b require only a small capacitance because theyare used to temporarily accumulate the magnetic energy discharged fromthe exciting coil.

Though this embodiment describes a 2-phase full-wave stepping motor, itcan also be applied to 3-phase, 4-phase, . . . , and n-phase full-wavestepping motors.

The present invention is used for the driving sources for robot arms andfor stepping movement of automatic-machine members.

I claim:
 1. A stepping motor comprising:an n-phase (n=2, 3, 4, . . . )full-wave rotor having salient poles; n-phase exciting coils installedon n-phase magnetic poles; semiconductor switching devices connected toboth sides of first, second, third, . . . , and n-th phase excitingcoils configured into first and first-bar exciting coils, second andsecond-bar exciting coils, third and third-bar exciting coils, . . . ,and n-th and nth-bar exciting coils, respectively; diodes respectivelyinversely connected to a series connection respectively comprising saidn-phase exciting coils and a transistor switch; a DC power sourceapplying voltage to said exciting coils through said semiconductorswitching devices; a first backflow-preventive diode, said first andfirst bar exciting coils connected to a positive or negative terminal ofsaid DC power source through said first backflow-preventive diode; anexcitation control circuit including said second and second-bar excitingcoils, said third and third-bar exciting coils, . . . , and n-th andn-th-bar exciting coils respectively excited by similarly-connectedsecond, third, . . . , and n-th backflow-preventive diodes, and thefirst, second, . . . , and n-th small capacity condensers connectedbetween the positive and negative poles of said DC power source togetherwith the back-flow-preventive diodes; a specified-frequency n-phasefull-wave stepping electric-signal generator; a first electric circuitgenerating a stepping torque by electrifying the semiconductor switchingdevices connected to respectively-corresponding said first, second,third, . . . , and n-th phase exciting coils by said stepping electricsignal; and a stepping electric-signal generator, said steppingelectric-signal generator comprising:a ROM including a digital memory; amemory circuit memorizing a specified number of steps; first and secondcounting circuits; a second electric circuit, operatively connected tosaid first and second counting circuits, inputting said specified numberof steps of said first counting circuits, inputting said specifiednumber of steps to said first counting circuit and half said number ofspecified steps to said second counting circuit; a third electriccircuit for starting subtraction of said first and second countingcircuits according to said number of specified steps, reading digitalmemory stores in said ROM, and inversely reading said digital memory ofsaid ROM by a zero-count output signal from said second counting circuitwhen the stepping motor starts; an oscillation circuit, connected tosaid ROM, converting the read signal from said ROM into an analog signalto obtain a frequency of oscillation pulse proportional to said analogsignal; a pulse distributor outputting n-phase full- or half-wavestepping electric signals by inputting the frequency of the outputoscillation pulse from said oscillation circuit; and a third electriccircuit, connected to said pulse distributor, for starting input of theoutput stepping electric signal from said pulse distributor to saidexcitation control circuit by a driving start command electric signal ofthe reluctance-type stepping motor and to stop inputting theoscillation-circuit pulse to said pulse distributor when said firstcounting circuit counts zero.
 2. A stepping motor comprising:an n-phase(n=3, 4, 5, . . . ) half-wave rotor having salient poles; n-phaseexciting coils installed on n-phase magnetic poles; semiconductorswitching devices connected to both sides of first, second, third, . . ., and n-th phase exciting coils; diodes respectively inversely connectedto a series connection comprising said n-phase exciting coils and atransistor switch; a DC power source, operatively connected to saidexciting coils, for applying voltage to said exciting coils through saidsemiconductor switching devices; first, second, third, . . . , nthbackflow-preventive diodes connected to a positive or negative pole ofsaid DC power source in a forward direction and to said semiconductorswitching devices for exciting said respective exciting coils; first,second, third, . . . , n-th small capacity condensers connected betweenthe positive and negative poles of said DC power source together withsaid first, second, third, . . . , nth backflow-preventive diodes; anexcitation control circuit including said second, third, . . . , andn-th backflow-preventive diodes, and first, second, third, . . . , andsaid n-th small capacity condensers; a specified-frequency n-phasehalf-wave stepping electric-signal generator; a first electric circuitgenerating stepping torque by electrifying said semiconductor switchingdevices connected to said respectively-corresponding first, secondthird, . . . , and n-th phase exciting coils by said stepping electricsignal; and a stepping electric-signal generator, comprising:a ROMincluding a digital memory; a memory circuit memorizing a specifiednumber of steps; first and second counting circuits; a second electriccircuit, operatively connected to said first and second countingcircuits, inputting said specified number of steps to said firstcounting circuit and half said number of specified steps to said secondcounting circuit; a third electric circuit for starting subtraction ofsaid first and second counting circuits according to said number ofspecified steps, reading digital memory stores in said ROM, andinversely reading said digital memory of said ROM by the zero-countoutput signal from said second counting circuit when the stepping motorstarts; an oscillation circuit, connected to said ROM, converting theread signal from said ROM into an analog signal to obtain a frequency ofoscillation pulse proportional to said analog signal; a pulsedistributor outputting n-phase full- or half-wave stepping electricsignals by inputting the frequency of the output oscillation pulse fromsaid oscillation circuit; and a third electric circuit, connected tosaid pulse distributor, for starting input of the output steppingelectric signal from said pulse distributor to said excitation controlcircuit by a driving start command electric signal of thereluctance-type stepping motor and to stop inputting theoscillation-circuit pulse to said pulse distributor when said firstcounting circuit counts zero.
 3. A stepping motor comprising:an n-phase(n=2, 3, 4, . . .) full-wave magnet rotor; n-phase exciting coilsinstalled on n-phase magnetic poles of a fixed armature; an excitationcontrol circuit including several sets of transistors including excitingcoils having various phases; a DC power source, connected to saidexcitation control circuit, for applying voltage to said excitationcontrol circuit; "n" backflow-preventive diodes connected to said DCpower source in a forward direction; diodes inversely connected inparallel to transistors of said circuit to return magnetic energy tosaid DC power source when said n-phase exciting coils are turned off; afirst electric circuit, connected to said excitation control circuit,for supplying power to the excitation control circuit and includingseveral sets of transistors through said "n" backflow-preventive diodes;a specified-frequency n-phase full-wave stepping electric-signalgenerator; an apparatus, connected to said excitation control circuit,for generating stepping torque by electrifying said excitation controlcircuit by said stepping electric signal; and a stepping electric-signalgenerator comprising:a memory circuit for memorizing a specified numberof steps; first and second counting circuits; a ROM; a second electriccircuit, connected to said memory circuit and said first and secondcounting circuits, for inputting said specified number of steps to saidfirst counting circuit and half said number of specified steps to saidsecond counting circuit; a third electric circuit, connected to saidfirst and second counting circuits, for starting subtraction of saidfirst and second counting circuits according to said number of specifiedsteps, reading a digital memory stored in said ROM, and reading backwardthe digital memory of said ROM by employing a zero-count output signalfrom said second counting circuit when the stepping motor starts; anoscillation circuit, connected to said ROM, for converting the readsignal of said ROM into an analog signal to obtain a frequency of anoscillation pulse proportional to said analog signal; a pulsedistributor, connected to said oscillation circuit, for outputtingn-phase full- or half-wave stepping electric signals by inputting thefrequency of the output oscillation pulse of said oscillation circuitand including an output stepping electric signal; and a fourth electriccircuit, connected to said pulse distributor, for starting input to saidoutput stepping electric signal of said pulse distributor to saidexcitation control circuit of the motor by the driving start commandelectric signal of the stepping motor and to stop inputting theoscillation-circuit pulse to said pulse distributor when said firstcounting circuit counts zero.
 4. A stepping motor comprising:an n-phase(n=3, 4, 5, . . . ) half-wave magnet rotor; n-phase exciting coilsinstalled on n-phase magnetic poles of a fixed armature; transistorsconnected to both sides of said exciting coils; diodes respectivelyconnected to a series connection comprising said n-phase exciting coilsand a transistor switch; a DC power source for applying voltage to saidexciting coils through said transistors; "n" backflow-preventive diodesconnected to said DC power source in a forward direction; an excitationcontrol circuit for respectively electrifying said n-phase excitingcoils through "n" backflow-preventive diodes; "n" condensers having aspecified capacity, respectively connected between output sides of said"n" backflow-preventive diodes and a negative pole of said DC powersource; a specified-frequency stepping electric-signal generator; afirst electric circuit, connected to said specified-frequency steppingelectric signal generator, for generating stepping torque byelectrifying said transistors connected to both sides ofrespectively-corresponding n-phase exciting coils by said steppingelectric signal; and a stepping electric-signal generator comprising:amemory circuit for memorizing a specified number of steps; first andsecond counting circuits; a ROM; a second electric circuit, connected tosaid memory circuit and said first and second counting circuits, forinputting said specified number of steps to said first counting circuitand half said number of specified steps to said second counting circuit;a third electric circuit, connected to said first and second countingcircuits, for starting subtraction of said first and second countingcircuits according to the said number of specified steps, reading adigital memory stored in said ROM, and reading backward the digitalmemory of said ROM by employing a zero-count output signal from saidsecond counting circuit when the stepping motor starts; an oscillationcircuit, connected to said ROM, for converting the read signal of saidROM into an analog signal to obtain a frequency of an oscillation pulseproportional to said analog signal; a pulse distributor, connected tosaid oscillation circuit, for outputting n-phase full- or half-wavestepping electric signals by inputting the frequency of the outputoscillation pulse of said oscillation circuit and including an outputstepping electric signal; and a fourth electric circuit, connected tosaid pulse distributor, for starting into to said output steppingelectric signal of said pulse distributor to said excitation controlcircuit of the motor by the driving start command electric signal of thestepping motor and to stop inputting the oscillation-circuit pulse tosaid pulse distributor when said first counting circuit counts zero.